icon.ico doesn't work

I wanted to set an icon and i found it must be in the .ico format, the icon is 64x64 and i called it "icon.ico" and i veryfied the image is really a .ico file, but when i try to put it in the game its says :
"Selected image isis not a valid '.ico' format"
why does it do that? i do like the tutorial guy did, what happened!? i need help!